int
crypto_generichash(unsigned char *out, size_t outlen, const unsigned char *in,
unsigned long long inlen, const unsigned char *key,
size_t keylen)
{
return crypto_generichash_blake2b(out, outlen, in, inlen, key, keylen);
}
int dfcrypt_decrypt(
const dfcrypt_state_t *state,
const unsigned char *ctxt,
size_t ctxt_len_bytes,
const unsigned char *message_number,
unsigned char *ptxt_out
)
{
const unsigned char *salt = ctxt;
const unsigned char *nonce = ctxt + DFCRYPT_INTERNAL_SALT_BYTES;
const unsigned char *encrypted = nonce + crypto_stream_chacha20_NONCEBYTES;
const unsigned char *ciphertext_mac = ctxt + ctxt_len_bytes - DFCRYPT_INTERNAL_MAC_BYTES;
unsigned char keys[DFCRYPT_INTERNAL_AKEY_BYTES + DFCRYPT_INTERNAL_EKEY_BYTES];
const unsigned char *akey = keys;
const unsigned char *ekey = keys + DFCRYPT_INTERNAL_AKEY_BYTES;
unsigned char computed_mac[DFCRYPT_INTERNAL_MAC_BYTES];
/* Derive the authentication and encryption keys. */
assert(sizeof(keys) == 64);
crypto_generichash_blake2b_salt_personal(
keys, /* output */
sizeof(keys), /* output length */
state->appseed, /* input */
state->appseed_length, /* input length */
state->key, /* key */
DFCRYPT_KEY_BYTES, /* key length */
salt, /* salt */
message_number /* personalization (can be NULL) */
);
/* Re-compute the MAC. */
crypto_generichash_blake2b(
computed_mac, /* output */
DFCRYPT_INTERNAL_MAC_BYTES, /* output length */
ctxt, /* input */
ctxt_len_bytes - DFCRYPT_INTERNAL_MAC_BYTES, /* input length */
akey, /* key */
DFCRYPT_INTERNAL_AKEY_BYTES /* key length */
);
/* Check the MAC. */
if (sodium_memcmp(computed_mac, ciphertext_mac, DFCRYPT_INTERNAL_MAC_BYTES) != 0) {
return -1;
}
/* Decrypt the plaintext. */
crypto_stream_chacha20_xor(
ptxt_out, /* output */
encrypted, /* input */
ctxt_len_bytes - DFCRYPT_CIPHERTEXT_GROWTH, /* input length */
nonce, /* nonce */
ekey /* key */
);
return 0;
}
void dfcrypt_encrypt(
const dfcrypt_state_t *state,
const unsigned char *ptxt,
size_t ptxt_len_bytes,
const unsigned char *message_number,
unsigned char *ctxt_out
)
{
unsigned char *salt = ctxt_out;
unsigned char *nonce = ctxt_out + DFCRYPT_INTERNAL_SALT_BYTES;
unsigned char *encrypted = nonce + crypto_stream_chacha20_NONCEBYTES;
unsigned char *mac = encrypted + ptxt_len_bytes;
unsigned char keys[DFCRYPT_INTERNAL_AKEY_BYTES + DFCRYPT_INTERNAL_EKEY_BYTES];
const unsigned char *akey = keys;
const unsigned char *ekey = keys + DFCRYPT_INTERNAL_AKEY_BYTES;
/* Sample a random salt and nonce. */
randombytes_buf(salt, DFCRYPT_INTERNAL_SALT_BYTES);
randombytes_buf(nonce, crypto_stream_chacha20_NONCEBYTES);
/* Derive the authentication and encryption keys. */
assert(sizeof(keys) == 64);
crypto_generichash_blake2b_salt_personal(
keys, /* output */
sizeof(keys), /* output length */
state->appseed, /* input */
state->appseed_length, /* input length */
state->key, /* key */
DFCRYPT_KEY_BYTES, /* key length */
salt, /* salt */
message_number /* personalization (can be NULL) */
);
/* Encrypt the ciphertext. */
crypto_stream_chacha20_xor(
encrypted, /* output */
ptxt, /* input */
ptxt_len_bytes, /* input length */
nonce, /* nonce */
ekey /* key */
);
/* Append the MAC. */
crypto_generichash_blake2b(
mac, /* output */
DFCRYPT_INTERNAL_MAC_BYTES, /* output length */
ctxt_out, /* input */
DFCRYPT_INTERNAL_SALT_BYTES +
crypto_stream_chacha20_NONCEBYTES + ptxt_len_bytes, /* input length */
akey, /* key */
DFCRYPT_INTERNAL_AKEY_BYTES /* key length */
);
}
